Machine tools conventionally employ metalworking or cutting fluid to lubricate and cool the cutting interface between the tool and the workpiece. These fluids serve the purpose of cooling and lubricating and in addition carry away the shavings and chips of material cut from the workpiece.
Metalworking facilities typically employ a number of cutting tools, many of which require similar metalworking fluids. Such facilities often employ what is referred to as the metalworking fluid central system. The central system collects and stores the metalworking fluid from a plurality of machine tools in a common reservoir and filters and recirculates the fluid between the reservoir and the tools.
In many metalworking applications, it is preferred to utilize water-based cutting fluids to take advantage of a higher heat absorption capacity than that provided by oils and non-soluble fluids. In addition, water-based fluids are preferred in many applications because they are less likely to contaminate the air and other aspects of the working environment within the facility. In addition, many water-based fluids are more economical, particularly when it is taken into account that they are biodegradable and may be more easily disposed of than petroleum based or other oil or organic based fluids. In addition, water-based fluids are generally not as flammable or explosive and thus less hazardous.
Water-based fluids, however, introduce other problems. Water-based fluids are more susceptible to loss by evaporation, provide a medium for the growth of biological contaminants, and, because of their biodegradability, are prone to attack by the microorganisms which can grow within them.
Water-based metalworking fluids generally fall into three categories. In one category includes soluble oils which are generally mineral oil. Another type of water-based metalworking fluid is the semi-synthetic fluid which is made up in part of mineral oil and in part by a combination of other synthetic lubricants. A third type of water-based metalworking fluid is the synthetic fluid which is made up entirely of synthetic components. The choice of cutting fluid is usually dictated by the particular machine operation and materials being worked.
With water-based metalworking fluids, a number of components are added to the water-based fluid solution in addition to the soluble oil or synthetic lubricant which provides the basic lubricating function. The additives include corrosion inhibitors which will coat the workpiece, the removed chips and the other metallic parts of the tools and other machine components which are subject to oxidation. In addition, emulsifiers are added to retain and disperse the oils throughout the solution so that they are available to provide lubrication at the point of cut. Corrosion protection is usually provided by the introduction of organic salts into the solution. Microbiocides are also an important component of water-based metalworking fluid systems. The water-based medium, in addition to the organic lubricant which provides food for microorganisms, requires biocidal ingredients to inhibit the growth of bacteria and mold. Other specific components are also required for various specific applications to maintain the appropriate fluid properties to cool and lubricate the particular cutting operation. The addition of buffers are added as well as caustic or other substances to control or alter the pH of the fluid.
Important in maintaining central systems is the desire that the properties of the cutting fluid be kept within controlled limits. The operating domain of the cutting fluids is generally a hostile environment in which many factors are at work which alter and degrade the cutting fluid. In addition to an overall degradation of the fluid, many specific cutting fluid properties and components are disproportionately affected when the environmental factors are allowed to act on the fluid. In addition to degradation of the fluid, loss of fluid occurs through evaporation, through the splashing out of fluids from the system, and from the carrying off of fluids on the parts and on the chips which are carried away. This may change the fluid volume and may also change the concentration of the various fluid components.
Evaporation, for example, will cause a loss of the water and also a loss of various fluid components in relation to their volatility. The carry-off phenomenon is more likely to deplete the lubricating oil component of a fluid which adheres to the parts and chips which are removed from the system. This is most often responsible for a loss in concentration of the corrosion inhibitors which, by their nature, adhere to the parts and the metal chips. Accordingly, make-up water must be added regularly. Oil or lubricant concentrates must be added to maintain their concentration in the fluid solution. Corrosion inhibitors must also be added to the fluid to compensate for their selective depletion.
The reservoirs of most central systems are usually located below floor level and thus are easily contaminated with bacteria and mold laden material. Such microorganisms breed in the solutions, attacking the emulsifiers, corrosion inhibitors and lubricant materials of the metalworking fluid. In addition, other lubricating and hydraulic oils and other foreign materials enter the metalworking fluid, some becoming emulsified within the fluid. These generally are a detriment to the fluid's performance and to the duration of its life.
Maintenance of a metalworking fluid central systems requires a controlling of the various properties and components of the metalworking fluid. Loss of cooling and lubricating capacity of the fluid can produce expensive and damaging results by increasing the production of scrap and by decreasing the life of tools and other machine components. A failure to control the properties of the fluid which prevent corrosion of the parts and cuttings results in increased waste due to the corrosion. In addition, increased contamination of the system with oxidation products reduces the lubricating effects of the fluid and the fluid's useful life.
Furthermore, a serious problem with water-based fluids results from failure to control microbiological growth in the metalworking fluid. Microorganisms in the fluid will, up to a point, grow with increasing rapidity if their growth is not checked in an early stage. The growth of these organisms tends to alter the system pH and otherwise change the environment in such a way as to facilitate increased growth rate of the micro-organisms. Since microorganisms feed on the lubricating components and other organic components of the fluid, they degenerate or degrade the fluid to the point where it loses its ability to lubricate, protect the parts, or to otherwise perform its function. This can prematurely end the life of the oil, accelerating the need for a complete replenishment of the fluid in the system. Fluid replacement may involve significant downtime, substantial cost for the replacement fluid, and additional expenditures in disposal of the spent fluids in accordance with environmental criteria.
The methods employed in the prior art to determine the conditions of the fluid in order to respond to changes in the fluid conditions have been inadequate to properly maintain the fluid. The common method of monitoring the properties of metalworking fluids has been to extract a sample of the fluid from the system, remove it to a laboratory, and perform a wet chemistry analysis upon the sample. Such procedures are generally regarded as capable of performing an accurate analysis on the properties of the fluid at the time, and under the conditions upon which, the test is made. However, the procedures are slow and, in many cases, changes in the sample result between the time the sample is taken and the time at which it is analyzed. This method of testing often produces data which are out of date due to the testing delay or inaccurate due to the change in the property being measured subsequent to the drawing of the sample.
Accordingly, corrective action taken is often too slow or at the wrong level to correct for the actual condition of the fluid at the time the correcting action is carried out. Thus, the corrections have been insufficient, resulting in considerable instability in the fluid property maintenance. As a consequence poor fluid performance results. Furthermore, the prior art systems have not resulted in the collection of data regarding the fluid's properties in a combination sufficient to make it possible to detect and determine the causes of fluid problems and to indicate the appropriate corrective response.